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1999 Buick Park Avenue - Persisting Misfire Issue

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Old 05-11-2018, 07:39 PM
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Exclamation 1999 Buick Park Avenue - Persisting Misfire Issue

I recently purchased a 1999 Buick Park Avenue Ultra w/ 3.8l 3800 Series II Supercharged V6 with 200,000 miles. When I purchased it, was throwing a P0302 code (Cylinder 2 misfire). The car was a good price and I (wrongfully) assumed the misfire was likely just a simple plug/wire related issue, so I bought it. Immediately after purchase, I:
-Changed the oil
-Swapped in new spark plugs
-Swapped in new plug wires
-Swapped in new coil packs
None of these repairs fixed the misfire, however.

The misfire itself comes and goes - one day the vehicle will drive fine with ndo issues, and the next, it will act up furiously and misfire very aggressively as I'm driving it. The other day, I had just started the vehicle up when I noticed it was acting very sluggish - as if it was having trouble pulling in air. I gave it a little gas and the engine stalled out at around 40mph, and wouldn't allow me to turn it back on afterwards. I didn't have my code reader but it was flashing the "Check Engine" light and dinging at me. I had been driving for less than a minute. I know a little bit about cars, but I am far from an expert, so I am not sure if these two issues are related? Additionally, the car will have difficulty starting up sometimes. Sometimes, it will grind as if the starter is going out, but again, other times, it works fine and starts up immediately.

I have performed the following maintenance on it attempting to solve the misfire/stall issue, but none of it has solved the problem.
-Replaced fuel injectors with refurbished injectors out of a 1997 Park Avenue W/O supercharger (cleaned them + new O-rings/pintle caps)
-Replaced throttle body gasket
-Replaced intake manifold gasket
-Replaced fuel pump
-Replaced ECM
-Tested Mass Air Sensor (it was fine)
-Tested Crank Position Sensor (it was also fine)
-Tested battery (it was fine, reading between 12.8 to 14.0 volts)

I am beginning to think that the problem must be within the wiring harness. Does anyone have any ideas where to start looking and if those issues mentioned above would all be related to a short? Or, does anyone have any other ideas before I start that job?

Thanks in advance.
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Old 05-12-2018, 10:38 AM
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If you don't mind me asking...what is a "good" price for a 20 year old Buick with 200k miles?
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Old 05-12-2018, 11:12 AM
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Originally Posted by Mad_Coachman View Post
If you don't mind me asking...what is a "good" price for a 20 year old Buick with 200k miles?
It was $750. Other than the mileage the car is in good shape. Had a new transmission put in at 140k. Left me some room to have funds to work on it.
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Old 05-12-2018, 02:15 PM
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One immediate concern is that the supercharged application uses different injectors than the naturally aspirated application (higher flow rate).

I would be checking compression as the next step, because you have ruled out both spark and fuel related concerns on this one cylinder.
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Old 05-12-2018, 03:14 PM
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Originally Posted by rjolly87 View Post
One immediate concern is that the supercharged application uses different injectors than the naturally aspirated application (higher flow rate).

I would be checking compression as the next step, because you have ruled out both spark and fuel related concerns on this one cylinder.
Damn, alright, I'll get right on swapping those injectors back in. I read somewhere that they were compatible but I suppose you can't believe everything you read (especially when you're hoping it'll save you $450). The issue has not changed since before and after the injector swap, however.

I just ran the compression and it'* coming back normal, 8.5:1. Any advice moving forward?
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Old 05-12-2018, 09:31 PM
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As a general rule, injector/compression problems don't go away.....so when you say it runs great one day and may be a dog the next, I tend to think it is either a wiring problem, ICM problem, crank or cam sensor problem, or PCM problem.....

No other code besides the P0302?
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Old 05-12-2018, 11:44 PM
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Originally Posted by Tech II View Post
As a general rule, injector/compression problems don't go away.....so when you say it runs great one day and may be a dog the next, I tend to think it is either a wiring problem, ICM problem, crank or cam sensor problem, or PCM problem.....

No other code besides the P0302?
Nope, it hasn't thrown any other codes which is frustratingly vague. I swapped the PCM/ECM (contained as the same unit on this car) & tested the crank sensor, and also swapped the ICM which didn't solve the problem (it has the old one back in it - I just tested it by swapping another one in- forgot to mention this in my initial post).

I'll check out the cam sensor tomorrow and report back, but I agree, it'* starting to look like a wiring issue to me, which is fantastic because hunting down bad wires is probably the bane of my existence. Any advice on where to start? Should I just begin at the #2 injector wire and follow it back to the ECM, or are there other places I'll need to look, too? Thanks.
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Old 05-13-2018, 12:32 PM
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With the engine running, I would SAFELY, tug on any wire harness I could reach, to see if it affects the operation of the engine....
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Old 05-15-2018, 02:55 PM
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Check fuel pressure at idle. Disconnect vacuum hose from fuel pressure regulator. Does fuel pressure change? Let us know before and after.

Could be a flaky fuel-pressure regulator, although it would be weird for it to affect one cylinder.
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Old 05-15-2018, 08:59 PM
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I almost forgot.....have you check the PCM and the wires to it?
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